That's wrong. Debian stable aims at production systems. If your
arguing would be true I wonder why stable contains applications like
Openoffice.org or audio players or ...

IMO multimedia users can/should live with
testing without any fear of system crashes and security updates.

I guess there are multimedia users out there who care much about a
stable system, reproducible results and have to earn some money from
their work - so they do not want to deal with unforseable changes.
Please do not advertise testing as a release which is ready for
users. (Yes, I admit I use testing in the way you describe - but
*I* know what I'm doing.)

But is not that big problem to install two kernels? One, the default
Lenny kernel and an RT kernel from testing?